In general, the next generation communication system has evolved to provide mobile stations with services capable of high-speed, high-capacity data transmission and reception. Therefore, the next generation communication system is developing into an orthogonal frequency division multiplexing communication system using a multiple input, multiple output scheme (i.e., a MIMO-OFDM communication system) to enable high-speed, high-capacity data transmission and reception.
In a MIMO-OFDM communication system, a signal transmission apparatus (e.g., a base station) exchanges signals with a signal reception apparatus (e.g., a mobile station) according to a frame structure. Therefore, the Base Station (BS) and the Mobile Station (MS) should acquire synchronization therebetween for the signal exchange according to the frame structure. For synchronization acquisition, the BS transmits a preamble signal so that the MS can detect a start of the frame transmitted by the BS. The MS receives the preamble signal transmitted by the BS, detects frame timing of the BS from the received preamble signal, and demodulates the frame received according to the detected frame timing. The preamble signal is used not only for the synchronization acquisition between the BS and the MS, but also for channel estimation between the BS and the MS.
In a MIMO-OFDM communication system, the schemes for generating a preamble signal can be roughly classified into a block-type scheme (or block-type preamble signal generation scheme) and a comb-type scheme (or comb-type preamble signal generation scheme). A description thereof will be given below.
Block-Type Scheme
A block-type scheme, also known as a pilot symbol scheme, refers to a scheme of generating a preamble signal using all subcarriers included in a corresponding OFDM symbol as a pilot tone, or pilot subcarrier, for a predetermined OFDM symbol period (e.g., M-OFDM symbol period).
Comb-Type Scheme
The comb-type scheme, also known as a pilot subcarrier scheme, refers to a scheme of generating a preamble signal using a predetermined number of subcarriers among the subcarriers included in each OFDM symbol, as a pilot tone.
A description will now be made of a channel estimation scheme for the MIMO-OFDM communication system that uses the block-type scheme as the preamble signal generation scheme.
Generally, the MIMO-OFDM communication system, when using the block-type scheme as the preamble signal generation scheme, uses a channel estimation scheme such as a Least Square (LS) scheme or a Minimum Mean-Square Error (MMSE) scheme. When the MIMO-OFDM communication system, using the block-type scheme as the preamble signal generation scheme, uses the MMSE scheme as the channel estimation scheme, the channel estimation performance is susceptible to noises, and the calculation complexity increases due to the auto-covariance matrix and cross covariance matrix calculations. In addition, when the MIMO-OFDM communication system uses the LS scheme as the channel estimation scheme, the system should use it along with a linear interpolation scheme because it should consider all channels between transmit antennas used in the BS and receive antennas used in the MS. In this case, the channel estimation performance may deteriorate due to the use of the linear interpolation scheme, and in particular, the channel estimation performance may considerably decrease with an increase in the number of transmit antennas and the number of receive antennas.
In addition, although the MIMO-OFDM communication system, using the block-type scheme as the preamble signal generation scheme, uses the MMSE scheme as the channel estimation scheme, the calculation complexity is very high, and the high calculation complexity may serve as overload of the channel estimation.
Therefore, there is a need for a channel estimation scheme for reducing the calculation complexity without the performance degradation in the MIMO-OFDM communication system using the block-type scheme as the preamble signal generation scheme.